I'm also being told by Parkview BMW not to use the shell gas right now as they just increased the cleaning agent in there gas by 20% few weeks a go.
Some BMW's are not reacting well to it.
Something to think about.

I find this funny as my wife was told recently by Parkview to use Shell or Esso only in her 335is as other fuels were causing problems.especially the 94 Petro Canada I do know that the turbo v8's are having issues with our crap fuels with extremely high underhood temps and have suggested using 87 octane instead of 91 to help with this issue.